Cannot browse neighborhood

I have 2 XP Pro machines and one Vista machine wired into a Netgear WNDR3700 router.
Client reports she can no longer connect to shared drives on Vista machine from machine A.
I find on arrival, that this true in addition she cannot find any machines in the Workgroup including A. Mapped drives to an older XP Pro machine still works, as do mapped drives on B to A.
Both XP's are running SP3 and updated. A has Norton's Security suite an B has MS Security Essentials with firewalls turned off.
I determine I can ping all devices on network, other machines, gateway, printers, music devices, and even localhost. I can map drives using IP addresses \\192.168.xxx.xxx\sharename.
A had some malware on it, but just your typical tracking cookies, nothing serious according to MBAM (note Norton's said it was clean).
Digging deeper, found on A that in "Services", Computer Browser was disabled and Server was running.. I enabled Browser, and now I can see machine A in Workgroup, but nothing else. On B, all services are running correctly. I still cannot see anything on network from B, including itself.
The Vista machine is totally invisible to browsing from either machine. The Vista machine does not see either of the XP machines, but finds my WIN 7 laptop and another WIN 7 laptop just fine. The WIN 7's do not see the XP's either.
They are all in the same workgroup, and have been networking fine for years.
They all get on the internet fine.
Only changes to the computer other than data, is updates.
I did "Enable NETBIOS over TCP/IP" on the network adapters.

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One thing that can happen with some malware is the IRPStackSize changes on XP and previous machines. This inhibits peer-to-peer connections. Here is an article about it http://www.howtonetworking.com/winissues/irpstacks ize.htm . Default number is 15 if I remember right on XP - I had a machine where it did a hidden set to 2 with malware. Try setting to 15 or 20 and see what happens.

This appears to be another of Windows' frustrating bugs. I have the same problem.

I uninstalled Trend Micro and went with Avast, and it helped. I can now see one of my two XP machines.

I then installed a Hotfix that MS calls "XP SP4" - they make you special request it and give you a password to unlock the zipped file. It solves (they say) a LLTD (Linked Layer Topology Discovery) problem.

Well, IT DOESN'T! I still can't "See" my XP laptop - although when I type \\JIMLAPTOP it connects.

I have lived with the frustration for MONTHS!

Please let me know if you finally find a "Fix".

BTW - I am using two switches off my router, but the XP Laptop is directly connected to the router.

I had a similar problem not long ago with XP and Win 7 machines. Make sure the following services are running: Computer Browser, Windows Firewall, Terminal Services, Server and Workstation.

On some Windows machines if you turn off the Windows Firewall service the Computer Browser service will turn off after 5 minutes. If you have a copy of Norton, uninstall and try to see if you can see the other computers.

I hope to be able to get to client's site today.
I need to check some ideas from this list.
In Control Panel, and in Nortons it is marked off.
Static IP addresses.
TCP/IP are correct.
Connections are good as ip ,pinging, printing to network printers work fine.
Thanks,
Dan